1. Field of the Invention
The present invention relates to endocardial electrodes for intra-cardial stimulation of the heart and/or for sensing heart signals.
2. Description of the Prior Art
Endocardial electrodes for stimulating and/or sensing signals from heart tissue are known in the art, generally consisting of an elongated flexible electrical conductor externally covered by an insulating sheath and having an internal channel for the introduction of a mandrin. Such electrodes have at least one electrode head for contact with the heart tissue disposed at the distal end of the conductor.
When implanting endocardial electrodes, for example in the atrium or at some other location to which access is difficult, it is frequently necessary that the electrode line be curved in certain regions. An electrode having a curved J-shape for stimulating the atrium, for example is known from U.S. Pat. No. 4,402,328. This electrode is permanently pre-shaped. For introduction through a vein, such electrodes are first stretched so as to be substantially straight by means of a mandrin, and the distal end of the electrode assumes the intended curvature when the mandrin is retracted.
Another possibility for inserting electrodes at locations to which access is difficult, is the use of specially pre-shaped mandrins. Whether the electrode or the mandrin is pre-shaped, the curvature of the electrode cannot be modified once the electrode has been placed in the heart, or during introduction of the electrode to the heart. With the use of a mandrin, variations within certain limits can be achieved by having mandrins of different shapes available. For this purpose, however, it is necessary to completely withdraw the mandrin from the electrode and either re-introduce the same mandrin after changing the shape thereof, or replacing one mandrin with a different mandrin having a different contour.
In conventional electrode structures, a further disadvantage exists in that the shape of the pre-formed electrode may not be optimum for every heart and for every type of use. Moreover, an electrode line which is not pre-shaped, but is instead bent by special mandrins, does not remain in this desired shape without undertaking further steps after the mandrin has been withdrawn.